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I am trying to figure out how I can actuate a high amperage 12V relay with only the batteries I have on board.

Basically the idea is here to have a 3.7V lithium cell, a momentary switch to actuate the relay, and then let the current flow from the lithium cell through the relay to the load.

Is there any way I can do this? I'll be dealing with loads up to 60 ampere, and a lithium polymer battery that can support that kind of discharge.

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  • \$\begingroup\$ Can you explain better your application? It seems to me that a relay is not needed at all. Tell us what you want to obtain, not what you think is a good way to obtain it. \$\endgroup\$ Aug 4, 2014 at 20:44
  • \$\begingroup\$ The answers you've been given are fine, but a 60A relay will probably require several watts of coil power, so your battery will have to supply that even if your load is very light. \$\endgroup\$ Aug 4, 2014 at 20:57
  • \$\begingroup\$ Is there a specific reason for using a mechanical relay? Would you consider power MOSFETs instead of a relay? 3.7V and 60A is within the capability of power MOSFETs. \$\endgroup\$ Aug 4, 2014 at 21:03
  • \$\begingroup\$ To be clear, the application will draw just under 60 ampere. I have considered using MOSFETs, but the voltage drop that will occur is not really acceptable from what I understand, I am likely to lose half a volt- which is significant in this specific application \$\endgroup\$
    – MildotPhil
    Aug 4, 2014 at 22:13
  • \$\begingroup\$ Many MOSFET can be wired in parallel to get as low ohm and low v drop as one like. \$\endgroup\$
    – EEd
    Aug 4, 2014 at 22:25

2 Answers 2

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This can boost 3.7 to 12V, about 1 to 2A. Enough to drive sizable relay.

Not sure if relay is needed. Can simpler mechanical switch do?

http://www.coolcomponents.co.uk/adjustable-4-12v-step-up-voltage-regulator-u3v50alv.html#.

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  • \$\begingroup\$ Well, it needs to be compact. I can't seem to find a DC momentary switch that can handle the amperage (that is also not giant) \$\endgroup\$
    – MildotPhil
    Aug 4, 2014 at 21:07
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    \$\begingroup\$ For same capacity, switch likely smaller than relay. Ampere capacity depends on contact point size. Mechanical switch is contact plus 'pusher'. Relay is same contact plus coil, which likely bigger than simple 'pusher'. \$\endgroup\$
    – EEd
    Aug 4, 2014 at 22:24
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So your relay coil voltage is 12V or 5V? Sounds like you need a boost converter to boost from your minimum cell voltage to the coil voltage, sized for the coil current. Something like the TPS81256 module from T.I. for example if your coil voltage was 5V and 550mA was enough current. It includes input and output caps as well as the inductor on a tiny PCB.

http://www.ti.com/lit/ds/symlink/tps81256.pdf

If you need more current, the TPS61230 should be good for a couple amps at least, and you can order a pre-built evaluation board from TI:

http://www.ti.com/lit/ds/symlink/tps61230.pdf

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  • \$\begingroup\$ That was my original thought, to use a boost converter. I'll just get something inline and make it happen. \$\endgroup\$
    – MildotPhil
    Aug 4, 2014 at 21:10

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